The naval fortress Kungsholmen is the world's oldest continuously fortified military installation as it has been manned since the 1600s. This fortress, together with the fortress at Drottningskär, was supposed to defend the main entrance to Karlskrona. Even up to late 1990s the fortress still played a significant role in the defense of Karlskrona from submarine intruders, and some remains from that defense activity can be seen in the North West as an old steel tower used to house surveillance cameras remotely operated from Kungsholmen.

Karlskrona, which can be seen straight up north, is part of the world heritage.